Explore the vast range of titles available.

Recent experiments have confirmed the compatibility of extended boron particulate injections with high performance plasma discharges in the full tungsten (W) environment of WEST. Utilizing an impurity powder dropper (IPD) equipped with boron (B) powders a series of extended experimental programs providing controlled injections have quantified plasma response to varying levels of injection rate and total injection quantity. Calibration of injection quantities confirmed through post-situ testing of the IPD and cross-correlated with both high-speed camera illumination and spectroscopic measurement have allowed for the first time a fine scale determination of the effects of powder introduction on plasma performance. Plasma enhancement, consistent with turbulence reduction through profile modification, has been observed with sustained increases in the stored energy (WMHD), by 18%, electron temperature (Te) by 35%, and neutron rate (Nn) by up to 200%, all of which scale positively with increasing powder injection rates. These injections have also resulted in both prompt and extended reductions in native impurity content, decreases in post injection radiated power, and strong decreases in divertor deuterium signatures signifying a reduction in recycling suggesting enhanced boron layer formation which provides a reduction of source terms and leads to enhanced gettering of main ion and impurity sources.

The oxidation of iron has been studied at low temperatures (between 260 and 500 °C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 °C allowed to propose a growth mechanism of the scale.

Boron (B) powder injection is a potential alternative to glow discharge boronization as a wall conditioning method for tokamaks. This technique is currently being studied in WEST experiments, during which B powder is injected by an Impurity Powder Dropper developed by PPPL. In order to interpret and analyse experimental trends, and to help develop future experiments, a modelling workflow using a boundary plasma simulation (SOLEDGE-EIRENE) and powder ablation simulation (Dust Injection Simulator) was developed and tested. The effect of adding a B neutral source to simulated deuterium + oxygen (D + O) plasmas was compared to experimental data from the WEST C5 campaign, where B powder was injected in a dedicated experiment. While the impact of B injection on radiated power P rad measurements at the upper divertor was similar, there were significant differences in measurements of P rad , outer strike point electron temperature T e OSP and O-II line intensity at the lower divertor between experiment and simulation. This discrepancy suggests that those parameters were affected by phenomena not present in the simulations, with the most likely candidates being reduced D recycling and a reduced O sourcing from the divertor.

In order to limit the ecological impact of air traffic and its operating costs, the aeronautical industry is looking for improving engines efficiencies and substitutes to high density Ni-based superalloys. Thus, a wider use of Ti-alloys operating at higher temperatures is one of the developed solutions. Being able to predict as accurately as possible the oxidation behavior of Ti-based components at high temperatures appears therefore crucial to improve their sizing and durability. Analytical models based on the solid-state diffusion laws can be found in the litterature. They are fairly accurate in most cases, but they reveal some intrinsic limitations in specific cases such as temperature transients or thin components. Numerical models were later developed to break down these limitations. First results from a new numerical tool called “PyTiOx” (still under development are presented here. They confirm the intrinsic limitations of analytical models. In the case of thin samples, the numerical model predicts an increase of scaling kinetic when metal becomes O-saturated, whereas analytical models do not.

Ni–30Cr model alloy was used to study chromia-scale formation behaviour. During its formation the mass variation signal is weak and it is important to take specific care to measure oxidation kinetics by thermogravimetric analysis. Symmetrical design allows the determination of very small mass changes in compensating buoyancy effects and limiting measurement drift. The mass variation measurement comprises noise coming from different sources that affects the electronic signal. It must be minimised to improve accuracy. This involves keeping the room-temperature constant, strictly balancing the beam and minimising buoyancy effects. By this way it was possible to acquire kinetics and to measured rate constants, k p , in a range from 3.10 –5 to 3.10 –10 mg 2 .cm −4 .s −1 equivalent to 10 –12 down to 10 –17 cm 2 .s −1 . Oxygen partial pressure ( P O 2 ) was monitor and revealed an abnormal consumption of oxygen at the beginning of the thermal exposure. Experiments with an inert material showed parasitic reactions identified by mass spectrometry as combustion of impurities. As oxygen consumption is not only due to oxidation of the sample, corrosion kinetics can’t be deduced from it. Hence, to determine whether the oxygen supply from the gas is a limiting parameter, a model, which quantifies oxygen consumption by sample oxidation within the thermobalance, is proposed.

In support of the selection of structural materials for heat exchangers in helium-cooled high temperature reactors, the oxidation behaviour of the Ni-base chromia-former alloy 230 was investigated at 850 °C in diluted helium atmosphere with a low water vapour content. In such a media, the equivalent partial pressure of oxygen (imposed by the \\( P_H_2 O \\)/\\( P_H_2 \\) ratio) is very low (\\( P_O_ 2 ^eq \\) around 10−16 Pa). The equivalent partial pressure of oxygen has no straight influence on the parabolic rate constant (kp); on the other hand, \\( P_H_2 \\) and \\( P_H_2 O \\) demonstrate a complex influence on kp. Photoelectrochemistry analyses revealed that this oxide could simultaneously contain two types of cationic defects. Specific oxidation tests with D2O showed that the oxide scale also contains hydrogen. A mechanist model is proposed in order to describe the scale growth using both cationic defects. Those theoretical results show, at least qualitatively, how \\( P_H_2 \\) and \\( P_H_2 O \\) may concurrently influence the oxidation rate.

Alloy 230 was studied as possible interconnect material for high temperature vapor electrolysis (HTVE) application. For such a use, the main important requirements are good corrosion resistance and a low area specific electrical resistance (ASR). The samples were oxidized at 800 °C for 250 h under cathodic (Ar–1 %H2–9 %H2O) and anodic (dry air) HTVE atmospheres. In situ ASR evolution of alloy 230 in both conditions was determined using a specific device. The influence of a LaCrO3 coating is also discussed in this study. It is shown that alloy 230 offers good corrosion resistance, improved by the presence of the coating. A calculation of the theoretical ASR is in good agreement with the experimental value obtained in anodic environment. For the cathodic condition, the ASR value is two orders of magnitude higher than the expected one, and this could be explained by the presence of hydrogen in the oxide layer. The LaCrO3 coating effect on ASR values remains unclear, but it appears to have at least an influence on its evolution over the test duration.

The human HIV transactivator protein Tat is essential for efficient viral transcription that occurs by a complex mechanism involving interaction of Tat with the TAR RNA element. This interaction appears to require the mediation of a cellular protein, cyclin T1. However, the possibility that Tat and TAR associate in a binary Tat-TAR complex has been little investigated. Using a chemically synthesized active Tat protein, the kinetic and equilibrium parameters of its interaction with TAR were determined by surface plasmon resonance technology. Independently of partner and method of immobilization onto the sensor chip, the association (k(a) = 5-9 x 10(5) M(-1) s(-1)) and dissociation rate constants (k(d) = 1.7-4.3 x 10(-3) s(-1)) yielded similar equilibrium dissociation constants (K(d) = 2-8 nM). A truncated peptide encompassing residues 30-86 of Tat did not bind to TAR at all. We conclude that Tat can form a high-affinity complex with TAR in the absence of cyclin T1 and that the N-terminal domain of Tat is essential for this interaction, suggesting a conformational link between this domain and the basic domain of Tat. These results are important in our quest for developing therapeutic compounds that impair viral replication.